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Garage floors, shed pads and RV slabs built for their load
A slab under a garage, shed or camper does a different job than a patio. It carries concentrated weight, sometimes a building, and in a Wisconsin winter it takes whatever drips off a salt-crusted car every afternoon. Getting it right starts with an honest answer to one question: what will actually sit on this concrete, now and ten years from now? From there, the base, the thickness, the edges and the drainage follow. This page walks through each one so you can compare plans with confidence.
Start with the load, not the footprint
A shed full of garden tools, a two-car garage for sedans, a work truck with a loaded bed, a travel trailer and a motorhome all ask very different things of a slab. The area may be similar, but the weight on each wheel or post is not. Tell the contractor the heaviest thing that will ever park or stand on the pad, including anything you plan to buy later.
For light sheds and ordinary car traffic, a slab around four inches thick over a well-compacted stone base is common. Heavier vehicles and equipment typically call for a thicker slab, heavier reinforcement, or thickened areas where wheels or supports sit. These are design choices the contractor makes after seeing the site and hearing the loads, which is why the first conversation matters.
Detached garages and the alley-lot layout
Many older neighborhoods in and around Milwaukee put the garage at the back of the lot, reached from an alley. Replacing the floor of one of those garages often happens with the walls still standing, which means the work is done through the overhead door with limited room to maneuver. How the old slab is broken up and removed, and how new concrete will be delivered, are practical questions to settle up front.
A new garage built from scratch usually needs a foundation designed for the building as well as a floor slab. Rules on garage construction differ from one municipality to the next, so ask your city or village what approvals apply before design begins, including anything it expects for frost protection of the foundation.
Brine, drips and the garage floor in winter
Every car that comes home in January brings road salt with it. The slush melts off the wheel wells, pools on the floor and soaks into the surface, then freezes whenever the garage drops below freezing. That cycle is why so many garage floors around here flake near the door and under the wheel wells while the back of the slab looks fine.
Three things help. First, air-entrained concrete, which is standard practice for slabs exposed to freeze-thaw and salt. Second, a floor pitched toward the door or a drain so meltwater leaves instead of sitting. Third, a penetrating sealer applied when the contractor recommends, then renewed over the years. Squeegeeing slush out during thaws also makes a noticeable difference.
The apron, the strip just outside the door, gets the worst of it. It sees plows, freeze-thaw, and brine from both directions. Ask whether the apron and the floor will be poured as separate slabs with a joint between them, which makes a future apron repair far simpler.
Edges, joints and reinforcement under concentrated weight
Slabs tend to fail at their edges first, because an edge has support on only one side. Thickened edges are a common design for garage and shed slabs, and they also help where a building sits on the perimeter. Around the outside, soil or stone packed firmly against the edge prevents water from undercutting it.
Joints matter as much on a garage floor as on a driveway. Planned control joints divide the slab into panels so shrinkage cracks follow straight, tidy lines. Rebar or wire mesh set up in the slab keeps cracked panels from separating under heavy wheels. Ask how reinforcement will be supported during the pour, since steel pushed down to the base does little.
Shed and RV pads out in the yard
A shed pad sounds simple, and often is. The two decisions that matter most are where it sits and how it drains. A low corner of the yard collects water, and a slab there tends to heave and stay wet. Choose a spot that stays drier and keep the pad slightly above the surrounding grade so rain runs off it.
RV and trailer pads carry heavy weight on a few tires and jacks, sometimes parked for months. A thicker slab, stronger reinforcement and a solid approach from the driveway are typical. Plan the turning path too, because a camper that has to cut across the lawn to reach its pad will rut the grass and can crack the slab edge. Local rules on where large vehicles may be stored vary, so check with your municipality and HOA.
Curing a slab properly, including one poured in a cold garage
A slab gains most of its early strength in the first days and weeks, provided it stays moist and does not freeze. In summer, that means protecting it from drying too fast with a curing compound or covering. In spring and fall, when a detached garage can drop below freezing overnight, the contractor may cover the new floor with insulated blankets or plan the pour around the forecast. Keep vehicles off until the contractor says the slab is ready, and remember that cool weather slows the process.
What a complete slab quote should spell out
- The intended load, written down, so both sides agree on what the slab is built for.
- Excavation depth, base material, base depth and compaction method.
- Slab thickness, any thickened edges or pads, and the reinforcement type.
- Air-entrained concrete for exterior or garage exposure.
- Joint layout, slope direction and where water will exit.
- Removal of the old slab, access for equipment, and cleanup.
Garage floors, shed pads and RV slabs built for their load — common questions
Why is my garage floor flaking near the door?
That pattern usually comes from salt-laden slush melting off cars, soaking into the surface and freezing again. The front of the slab gets the most brine and the coldest temperatures, so it flakes first. Air-entrained concrete, a floor sloped so water leaves, and a penetrating sealer help on a new slab. For an existing floor, the contractor can advise whether resurfacing or replacement makes more sense.
What slab depth does a camper or motorhome need?
It depends on the vehicle weight, the soil and how the pad will be approached. Heavy vehicles generally need something thicker than a standard four-inch patio, with stronger reinforcement and a well-compacted base. The contractor should size it after hearing what you will park there. Give the actual weight and length of the RV, and mention whether it will sit for long periods on jacks or stands.
Can a garage floor be replaced without tearing down the garage?
Often, yes. Floors in detached garages are replaced with the walls standing by breaking out the old slab inside, removing it through the door and pouring a new floor. The contractor will check how the walls sit on the foundation and whether the building is supported by the slab itself, because that changes the approach. Clearing everything out of the garage ahead of time helps.
Does a shed need a concrete slab, or will gravel work?
Small, light sheds often sit well on a compacted gravel pad. A concrete slab makes more sense for larger sheds, workshops, anything with a floor that must stay flat, or storage of heavy equipment like a riding mower. In either case, drainage and a firm base decide how well it holds up. Check local rules on shed size and placement, which vary by municipality.
Should a new garage floor slope toward the door or a drain?
It should slope toward wherever water can safely leave. Most residential garages are pitched gently toward the overhead door so meltwater and wash water run out. Some have a floor drain, and whether one is allowed and how it must connect depends on local rules, so ask your municipality. A level floor may look tidy, but it lets brine pool under parked cars.
What should I clear out before a slab is poured?
Move vehicles, stored items and anything near the work area, and think about the path equipment and a concrete truck will take. Mark sprinkler lines, invisible pet fences and shallow cables you know about, and have public utilities located before digging through the appropriate locate service. Let neighbors know if an alley or shared drive will be blocked for part of a day.
Talk through your project
Start with the address, what you want poured or replaced, rough dimensions, and a few photos of the area and any existing concrete.
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